Process of pickling iron and steel



252. COMPOSITIONS,

UNITED STATES hummer PATENT OFFICE IRA. H. DERBY, 0F INDIANAPOLIS,INDIANA, ASSIGNOR TO PETER G. REILLY, OF INDIANAPOLIS, INDIANA PROCESSOF PICKLING LEON AND STEEL NI Drawin g.

My invention relates to the pickling of metal articles, particularlyiron or steel articles, or their alloys. More specifically, my inventionrelates to a process of reducing or inhibiting the solution of the metalarticle during the pickling operation.

In the manufacture of articles from iron, steel and their alloys, it isusual to subject the original ingot to a hot rolling step. For example,in the fabrication of steel plates, the original ingot is hot rolled toreduce the same to the desired size. During the process of working theingot, it becomes covered with a thin superficial layer of blue black,mainly ferro-ferric oxide. For satisfactory results in subsequentprocessing, as for example, cold rolling, it is necessary to completelyremove the oxide or scale as it is technically known, to develop a cleanmetallic surface. The cleaning may be accomplished mechanically bybuffing or polishing but this is laborious and expensive since the oxideis a harder material than the steel and is spread over a large surface.In View thereof, a chemical process is usually employed for removing theoxide scale. The process usually consists in dipping the article to becleaned in an acid bath as, for example, sulphuric acid, acid sulfates,preferably hot, or in cold dilute hydrochloric acid. The metal isallowed to remain in the cleaning bath for a short period of time,varying usually from ten to twenty minutes, after which it is withdrawn.Thereafter, the metal is washed with fresh water to remove that portionof the pickling solution adhering thereto. While this treatment effectsa loosening of the oxide scale in the form of small black to reddishbrown flocculent masses which fall away into the bath, it also allows aconsiderable amount of the metal to go into solution with anaccompanying liberation of hydrogen gas.

It may also be pointed out that in some cases, the excessive solution ofthe metal results in the production of a pitted surface instead of asatiny, smooth, uniform surface which is desired in the finishedcommercial article.

Application filed August 80, 1928. Serial No. 303,107.

the solution of the metal in the pickling bath to a minimum in order toavoid the loss of valuable material, and objectionable pitting.

I have discovered that phosphorous-sulfur compositions which maycomprise compounds or mixtures when added preferably in minute amounts,act to materially reduce or substantially prevent the solution in thepickling bath of iron or steel, or iron or steel alloys, and that at thesame time the removal of the scale is satisfactorily accomplished.Substances which function as described are known as inhibitors sincethey protect the 'iron or steel material being pickled from attack bythe pickling solution.

I have found that both soluble inorganic and organic phosphorous-sulfurcompounds function satisfactorily as inhibitors in the pickling of ironand steel articles. As an example of inorganic compounds the reactionproducts of nitrogen compounds with penta sulfide of phosphorous havegiven excellent results. For example, the reaction product of ammoniumhydroxide and penta sulfide of phosphorous have been found satisfactory.Various organic phosphorous-sulfur compounds may be used containingphosphorous and sulfur in combination with an aliphatic or aromaticradical. In the preferred form of my invention, I use organic nuclearphosphorous-sulfur compounds but, obviously, I do not desire to belimited to nuclear organic compounds. As an example of an aliphaticorganic inhibitor containing phosphorous and sulfur, satisfactoryresults have been obtained with the reaction product of phosphorouspentasulfideand an alcohol such as ethyl alcohol; The hoinologues of thelatter may be used to react with the pentasulfide as, for example, butylalcohol. Aromatic compounds, including hydrocarbons and substitutedhydrocarbons, such as phenols, cresols, xylenols, naphthols, theirhomologues," or mixtures of these compounds may be reacted withphosphorous pentasulfide to produce very satisfactory inhibitors.Excellent inhibitors may be produced by reacting phosphorouspentasulfidewith organic acids, aldeifides and ketones. Pentasulfide of phos- 50 Itis the object of my invention to reduce 'phorous may also'be treatedwith .nitrogen 1 derivatives such as the amines, nitriles and pyridinebases and the reaction products thereof used as inhibitors.

The following examples are illustrative of my invention:

1. Denatured alcohol was reacted with 20%, by weight, of phosphorouspentasulfide for an hour at its boiling point and the liquid reactionproduct was employed with the following results: An amount equal to .1'%of the pickling bath which consisted of 5% sulphuric acid was added. Thetemperature of the bath was raised to C. and a test piece of steel platewas immersed in the bath for fifteen minutes. The entire loss was foundto be .6% which represented the scale. The test piece was replaced inthe bath, maintained at the same temperature, for a subsequent period ofthirty minutes. A metal loss of less than 04% resulted. It is believedthat the major reaction product formed by the reaction of alcohol withphosphorous pentasulfide is tri ethanol tetra thio phosphoric acid.Howevifidonot desire to be limited to any specific reaction product butcontent myself with calling the reaction product that obtained by thereaction of alcohol with phosphorous pentasulfide.

2. Cresylic acid was reacted with 20%, by weight, of phosphorouspentasulfide for an" hour at 120 C. The liquid reaction product wasemployed with the following results: An amount equal to .1'% of thepickling bath which consisted of 5% sulphuric acid was added. Thetemperature of the bath was raised to 80 C. and a test piece of steelplate was immersed in the bath for fifteen minutes. The entire loss wasfound to be .6% which represented the scale. The test piece was replacedin the bath, maintained at the same temperature, for a subsequent periodof thirty minutes. A metal loss of less than 02% resulted. It isbelieved that the major reaction product formed by the reaction ofcresylic acid with phosphorous pentasulfide is tri cresol tetra thiophosphoric acid. However, I do not desire to be limited to any specificfinished reaction product bu content myself with calling the reactionproduct that obtained by the reaction of cresylic acid and phosphorouspentasulfide.

3. Benzaldehyde was reacted with phosphorous pentasulfide, giving anoily product. which was used in the quantity'of .1% of the picklingbath, yielding a metal loss of the order of .01'%. This example isbroadly representative of the preparation and use of the reactionproduct of an aldehyde and a phosphorous sulphur compound.

4. As representative of the ketone class of compounds, the following isgiven. At the boiling point of acetone, the reaction with phosphorouspentasulfide is relatively slow,

thereby producing a very dilute mixture of.

the active sulphur compound. This dilute mixture may be utilized as anaddition to the pickling bath. Satisfactory results were obtained whenthe acetone product was added to the bath in the amount of .1% of thepickling bath, the metal loss being of the order of 15%.

5. The following is an example of the use of amine reaction products.Aniline reacts rapidly with phosphorous pentasulfide and forms a solidproduct which is insoluble in water. This product, however, is solublein cresylic acid. A one to one mixture of the insoluble product was madewith the solvent and .1% of this solution, based on the weight of thepickling bath, was added to the bath, resulting in a metal loss of.07-%.

6. Benzonitrile was reacted with phosphorous pentasulfide, yielding aproduct which when added to the pickling bath in the amount of .1%,based on the weight of the pickling bath, gave a metal loss of the orderof .05%.

7. As is illustrative of the use of a pyridine base, the followingexample is given. A fraction of pyridine oil boiling between 210 and 280C. was obtained and reacted with 10% of phosphorous pentasulfide, givinga clear oil as a product. .1'% of this oil, based on the weight of thebath when added to the bath, gave a metal loss of 02%. It appeared tohave the same efimtive inhibiting property as the product formed byreacting cresylic acid with phosphorous pentasulfide.

8. Various hydrocarbons may be react-ed with phosphorous pentasulfide toform effective inhibitors. For example, naphthalene was heated to 200 C.with phosphorous pentasulfide, producing a resinous product insoluble inwater and therefore not in itself an inhibitor. The compound ofnaphthalene and phosphorous pentasulfide is soluble in cresylic acid.When dissolved in this medium and added in quantities of .1% to thepickling bath, a metal loss of the order of 02% was observed.Naphthalene has been given as an illustration of the use of an aromatichydrocarbon. However, the following hydrocarbons may also be reactedwith pentasulfide to produce a suitable inhibitor: coal tar distillates,including the lighter distillates, the heavier distillates, or theintermediate distillates, or a mixture of any or of all of thesedistillates, water gas distillates, oil tar distillates, Wood tardistillates and similar oils or mixtures thereof. Referring to the coaltar distillates, they may be used in the crude or refined state or afterthe addition thereto or the removal therefrom of various coal tarconstituents. Instead of using naphthalene anthracene may be used toreact with phosphorous pentasulfide to form an inhibitor. The compoundsreferred to above are merely illustrative of suitable hydrocarbons andare not to be 252. COMPOSITIONS,

taken as limiting the kind of hydrocarbon which may be used.

9. Phosphorous pentasulfide reacts with ammonia, producing a class ofcompounds which may be given the general name of thio phosphoric acidamines. These inorganic compounds form suitable inhibitors. For example,prosphorous pentasulfide was reacted with ammonium hydroxide solution,giving a product which was added in the quantity of 1% of the picklingbath. A metal loss of 13% was shown.

\Vhile I have set fort-h a number of methods for the preparation of thephosphoroussulfur inhibitors, they are obviously merely illustrative andnot by any way of limitation. I desire to point out that my inventionresides broadly in the addition of a soluble phosphorous-sulfurcomposition to the pickling bath to inhibit the solution of the articlebeing pickled regardless of the methods used for the preparation of theinhibiting agent. While I have given examples showing reactingaphosphorous-sulfur compound with an organic compound, it is obviousthat the inhibitor may be prepared by reacting a compound containingphosphorous with one containing sulfur. For example, an organic compoundmay have sulfur introduced therein and the sulphidized compound reacte-d with a phosphorous compound, or the organic compound may havephosphorous introduced therein and reacted with a sulphur containingcompound. Other analogous methods of preparation will readily suggestthemselves to those skilled in the art.

It is to be understood that my invention is not limited to the picklingof iron and steel per se but includes iron and steel alloys such aschromium alloys, nickel alloys, titanium alloys. and tungsten alloys.

While I have stated that in the usual case the percentage of inhibitoradded to the pickling bath is 1%, based on the weight of the bath, it isto be understood that this percentage may be considerably varied, eitherabove or below, depending on the character of the steel or alloy ofsteel being treated, and the efficiency of the inhibitor.

My invention may be practiced in connection with any of the picklingmediums or baths usually used. lVhile it is preferred to use sulphuricacid, examples of other suit able baths are acid sulfates andhydrochloric acid.

I claim:

1. The process of substantially preventing the solution of iron andsteel articles in a pickling bath comprising adding thereto a solubleinhibitor containing phosphorous and sulfur.

2. The process of substantially preventing the solution of iron andsteel articles in a pickling bath having sulfuric acid as its essentialconstituent comprising adding to LXEmIHB."

the bath a soluble inhibitor containing phosphorous and sulfur.

The process of substantially preventing the solution of iron and steelarticles in a pickling bath comprising adding thereto a relatively smallproportion of a soluble inhibitor containing phosphorous and sulfur.

4. The process of substantially preventing the solution of iron andsteel articles in a pickling bath comprising adding thereto a solubleorganic inhibitor containing phosphorous and sulfur.

5. The process of substantially preventing the solution of iron andsteel articles in a pickling bath comprising adding thereto a solublenuclear organic inhibitor containing phosphorous and sulfur.

6. The process of substantially preventing the solution of iron andsteel articles in a pickling bath comprising adding thereto a solublearomatic organic inhibitor containing phosphorous and sulfur.

7. The process of substantially preventing the solution of iron andsteel articles in a pickling bath comprising adding thereto an inhibitorconsisting of the reaction product of phosphorous pentasulfide and ahydroxy holding compound.

8. A pickling bath adapted to effect the usual cleaning of iron andsteel articles present therein and inhibit solution thereof, comprisinga pickling medium and a soluble inhibitor containing phosphorous andsulfur.

9. A pickling bath adapted to effect the usual cleaning of iron andsteel articles present therein and inhibit solution thereof, comprisingsulfuric acid and a soluble inhibitor containing phosphorous and sulfur.

10. A pickling bath adapted to effect the usual cleaning of iron andsteel articles present therein and inhibit solution thereof comprising apickling medium and a relatively small proportion of a solubleinhibit-or containing phosphorous and sulfur.

11. A pickling bath adapted to effect the usual cleaning of iron andsteel articles present therein and inhibit solution thereof, comprisinga pickling medium and a soluble organic inhibitor containing phosphorousand sulfur.

12. A pickling bath adapted to effect the usual cleaning of iron andsteel articles present therein and inhibit solution thereof, comprisinga pickling medium and a soluble nuclear organic inhibitor containingphosphorous and sulfur.

13. A pickling bath adapted to effect the usual cleaning of iron andsteel articles present thcrein and inhibit solution thereof, comprisinga pickling medium and a soluble aromatic organic inhibitor containingphosphorous and sulfur.

14. A pickling bath adapted to effect the usual cleaning of iron andsteel articles present therein and inhibit solution thereof,

comprising a pickling medium and the reaction product consisting ofphosphorous pentasulfide and ahydroxy holding compound.

15. A pickling bath adapted to efl'ectthe usual cleaning of iron andsteel articles present therein and inhibit solution thereof, comprisinga pickling medium and a soluble inhibitor containing phosphorous andsulfur in amount approximately equal to .1% of the weight of the bath.

In testimony whereof I have signed my name to this specification.

IRA H. DERBY.

